An out-of-control car blasted into an auto-body shop in Queens yesterday, killing one mechanic and chopping off the legs of another, authorities said.

Witnesses wrapped tourniquets around the 30-year-old legless victim’s thighs. He was listed in serious condition at New York Hospital Queens last night, officials said.

The mayhem began when Jim Hart’s Mercedesa boxing trainer was hit from behind by a Toyota Corolla, which then veered into the 126th Street shop near Citi Field at 11:40 a.m.

“It was bizarre because there were no other cars on the street,” Hart, 43, told The Post. “I kept wondering why he was hitting me. I figured maybe he was trying to rob me. He must have lost it.”

A mechanic was killed, another man lost his legs and a third victim suffered less serious injuries after a car slammed into an auto-body shop in Willet’s Point yesterday, authorities said.

Jim Hart, a boxing trainer from Astoria, said he was driving his 1998 black Mercedes Benz when a blue 1992 Toyota Corolla to the right and sharply to the left, around 11:40 a.m.

Hart tied a yellow rope around the legless victim to contain the bleeding, he said.

The Toyota also killed a 33-year-old mechanicthrowing him to the back of the shop and.

No one was charged yesterday.

The Toyota driver — who one witness said was speeding — got out of his car with a cane and stood expressionless in a pool of blood. The driver was taken away in an ambulance. Police did not release the names because family hadn’t been notified and no one has been charged.